ci: Disable test for i686 unknown linux target #652

Job	Run time
test (x86_64-unknown-linux-gnu, stable)	4m 29s
test (x86_64-unknown-linux-gnu, nightly)	4m 11s
test (aarch64-unknown-linux-gnu, stable)	2m 27s
test (aarch64-unknown-linux-gnu, nightly)	2m 6s
test (armv7-unknown-linux-gnueabihf, stable)	2m 22s
test (armv7-unknown-linux-gnueabihf, nightly)	2m 0s
test (riscv64gc-unknown-linux-gnu, stable)	2m 24s
test (riscv64gc-unknown-linux-gnu, nightly)	1m 51s
test (s390x-unknown-linux-gnu, stable)	2m 35s
test (s390x-unknown-linux-gnu, nightly)	1m 49s
test (x86_64-apple-darwin, stable)	1m 11s
test (x86_64-apple-darwin, nightly)	1m 18s
test (aarch64-apple-darwin, stable)	2m 28s
test (aarch64-apple-darwin, nightly)	2m 43s
test (x86_64-pc-windows-gnu, stable)	3m 32s
test (x86_64-pc-windows-gnu, nightly)	2m 29s
test (x86_64-pc-windows-msvc, stable)	5m 45s
test (x86_64-pc-windows-msvc, nightly)	5m 1s
test (i686-pc-windows-gnu, stable)	5m 11s
test (i686-pc-windows-gnu, nightly)	5m 25s
test (i686-pc-windows-msvc, stable)	3m 9s
test (i686-pc-windows-msvc, nightly)	2m 8s
	1h 6m 34s

Provide feedback